1. Field of the Invention
The invention is in the field of methods and devices for controlling solenoid valves.
2. Description of the Related Art
Prior methods of controlling solenoid valves have included voltage control and current control methods. Prior voltage control methods have pulled a solenoid valve with a voltage that is much greater than a lower hold voltage used to hold the solenoid valve engaged. The timing of the switch from the higher pull voltage to the lower hold voltage is based on adding a significant margin to ensure that pull takes place. In determining the margin the possibility of variations in solenoid inductance, the possibility of variations in solenoid resistance, and possible changes in voltage of batteries or other voltage supplies are all factored in to increase the margin of time that the pull voltage is applied. The result is one or more of wasted energy, overheated solenoids, varying switching times of solenoid valves, and/or the possibility of failure to engage (a situation where engagement of the solenoid valve is not achieved).
Prior current control methods involve measuring current through the solenoid, and adjusting this current to try to achieve a higher pull-in current and a lower hold current. This can reduce somewhat the added margin applied in voltage control. Changes in resistance and inductance will change the solenoid valve response times, but the current through the solenoid remains consistent. However a margin is added to the level of the pull-in current, and the pull-in time (the time that the pull-in current is applied) also generally has a margin added to it to account for variations in manufacturing of the solenoid valve and varying conditions. The result is still energy wastage, heating in the solenoid valve, and/or the possibility of non-engagement.
It will be appreciated that it would be desirable to come up with improved methods for solenoid control.